A visible image is formed in silver halide photographic materials by exposure of the material to actinic radiation to form a record of the exposure which is invisible to the unaided eye, followed by processing of the material to yield a visible image.
The visible record of exposure is referred to as a latent image. It is generally agreed that the latent image comprises minute specks of metallic silver formed in or on individual silver halide grains by interaction between silver ions and photoelectrons generated by absorption of actinic radiation by the silver halide grains.
Processing of most common silver halide photographic materials includes a development step in which the material is contacted with an aqueous alkaline solution of a developing agent. The developing agent is a reducing agent which will selectively reduce to metallic silver those silver halide grains containing a latent image.
It is known that the latent image is not permanent and that, with the passage of time, silver halide grains which would be devlopable immediately after exposure become nondevelopable. This phenomenon is termed latent image fading and manifests itself as a loss in image density in the developed image and a consequent loss in speed in the silver halide photographic material.
If silver halide materials were developed immediately following imagewise exposure, latent image fading would not be a problem. However, with many silver halide materials delays between exposure and processing frequently occur. For example, with amateur film materials in which multiple images are formed on a single roll of film there is often a delay of months between the time the first image is exposed and the time the exposed roll of film is sent for processing. With such materials latent image fading can present a significant problem and compounds are added to photographic materials to prevent or reduce it. These compounds are referred to as latent image stabilizing compounds or latent image stabilizers and the prevention or reduction of latent image fading is referred to as latent image stabilization.
Among latent image stabilizers known in the art are N-2-propenylbenzothiazolium and naphthothiazolium salts described in Arai et al U.S. Pat. No. 3,954,478. N-2-Propenyl substituent containing acyclic compounds useful as latent image stabilizers are disclosed in Herz U.S. Ser. No. 236,360, filed Feb. 20, 1981, SILVER HALIDE EMULSIONS CONTAINING LATENT IMAGE STABILIZING COMPOUNDS. Latent image stabilizers containing a 2-propynylthio substituent are disclosed by von Konig et al U.S. Pat. No. 3,910,791.
Prior to this present invention there has existed in the art a bias against incorporating compounds containing an amino-2-propynyl group into silver halide emulsions as addenda. Kuwabara and Iwai, "Effects of Acetylenic Derivatives on Photographic Emulsions", Bulletin of the Society of Scientific Photography of Japan, No. 16, December 1966, pp. 14-23, reports that compounds containing a 2-propynylamine group--i.e., 2-propargylamine and its substituted derivatives--produced fog in negative-working silver halide emulsions. On the other hand, if the 2-propynyl group is attached to a nitrogen atom of an unsaturated ring, fog was not produced (with one exception). Jagar et al U.S. Pat. No. 4,256,830 reports the effectiveness of certain 2-propynyl group containing compounds against color fog and reduced contrast, but in all instances of the 2-propynyl group attached to a nitrogen atom, the nitrogen atom is part of a ring. Adachi et al U.S. Pat. No. 4,115,122 discloses certain 2-propynyl substituted heterocyclic compounds to be useful as nucleating agents. In variant forms the 2-propynyl group is attached to the heterocyclic ring through an oxy linkage. In no instance is the 2-propynyl group attached to the heterocyclic ring through an amine linkage.